The present invention is a differential needle valve nozzle which is used in a fuel injection system in diesel engines, particularly used with locomotive engines, marine and electric power generation The fuel injection systems are often called unit injectors or EMD injectors (originally manufactured by the Electro-Motive division of General Motors).
The unit injectors typically have a nozzle valve body forming a tip or xe2x80x9cnosexe2x80x9d at one end. Another basic component of the fuel injector is the nozzle valve. The nozzle valve or xe2x80x9cneedlexe2x80x9d moves up and down within the nozzle body, alternatively opening and closing fuel ducts and spray holes through which fuel is sprayed.
One of the major problems faced by the diesel engine industry is the increasingly stringent standards for emissions to protect the environment from noxious gases which are a by-product of the internal combustion process. The U.S. Environmental Protection Agency (EPA) is particularly concerned about the amount of nitrogen oxides, carbon monoxide, hydrocarbons and other polluting gases from the engine exhaust.
The outside walls of the nozzle tip form an inverted dome. A cavity is formed inside the nozzle tip to receive the needle. The needle stops or seats on the needle""s down stroke when it strikes the inside walls of the nose. The location where the needle stops is the seat. In machining strikes the inside walls of the nose. The location where the needle stops is the seat. In machining the inside walls of the seat, a nipple or xe2x80x9csacxe2x80x9d is inevitably created. It is well known in the industry that reducing the sac volume of the fuel injection nozzles reduces the amount of hydrocarbon emissions. Fuel in the sac was forced out of the nozzle after injection was completed, entering the combustion cycle at a time when it could not burn. The fuel passed through the cycle causing unburned, polluting emissions.
The problem faced by the industry is how to minimize the sac volume while maintaining a constant wall thickness, maintaining the spray hole location and other design constraints. It is also desirable to maintain the ratio of the length over the diameter of the spray holes as a prescribed constant.
Prior art patents, e.g. U.S. Pat. 5,467,924, disclose a fuel injector with a reduced sac volume. The present invention accomplishes the delivery of fuel with no sac, or a sac which is minimal, substantially reducing the sac over any prior design.